Muscles are your body’s movers and shakers. They let you do everything from climbing a flight of stairs to chewing on a piece of beef jerky. But despite their obvious importance, most people have a rather strange way of treating their muscles. Some of us head to the gym and strain them for hours (mostly the stair-climbing muscles, not the beef jerky–munching ones). The rest of us spend more time worrying about other body parts—like the heart and the brain—and assume that our muscles will quietly adapt themselves to the demands of our day-today lives.

This is unfortunate, because the health of your muscles is vitally important to the health of your body. Even if your idea of a marathon is watching 12 back-to-back episodes of Gossip Girl, and the only powerlifting you do is moving groceries from the backseat of your car to the kitchen, you can’t afford to ignore your muscles. Strong, well-maintained muscles improve your blood pressure, your bone mass, and your ability to burn calories. They also reduce your likelihood of injury and the risk factors for countless diseases.

Meet Your MusclesFrom a biologist’s point of view, a muscle is a tissue that contracts. Your arm muscles contract to swing a racket and propel a ball across a tennis court. Less glamorously, the muscles in your lower intestine contract to ropel Sunday breakfast down your digestive tract. And if you’re a woman about to give birth, your uterus muscles contract to do something truly miraculous—squeeze a brand-new person out into the world. All these examples have a common theme: when muscles contract, things happen. Even if you think you’re neglecting your muscles, they never truly get a moment’s rest. Right now, for example, they’re hard at work on a thousand small but essential jobs—pumping blood through your arteries, directing your eyes over the words in this sentence, and keeping your body from slumping over onto the floor.

Part of the reason muscles work so well is because your brain keeps them busy all the time with tiny, partial contractions called muscle tone. This activity ensures that your muscles are healthy and always ready to act. If your brain stops doing its job—which can occur, for instance, in the event of a spinal injury—your muscles become floppy and begin to waste away.

The actual biochemical process that triggers a muscle contraction is quite complicated and, like all chemical reactions, it’s not entirely efficient. In fact, as much as 60 percent of the energy that fuels your muscle movements escapes as heat. That’s why the quickest way to warm up on a cold day is to jump up and down. It’s also why your body forces your muscles to start contracting when your body temperature drops—a phenomenon we call shivering.

Forest management comprises the use of science, economics, and social principles to maintain healthy forests. While forest management used to be an arm of the timber industry, today it includes other aspects for the purpose of conserving forests: creating sustainability in forests; multiple uses for individual forests, which conserves total forested land; fire management; and conservation of biodiversity. Forestry includes conservation methods also, but forestry’s objectives strive for the best ways to use trees as a natural resource for making products. Quite a bit of controversy has emerged when the two fields’ different objectives are not compatible. In a general sense, forest conservation can be divided into those who seek to protect the world’s remaining forests from any further destruction for any reason versus those who seek to find the most efficient ways of harvesting forests to meet the population’s growing needs for wood products. Even the most committed activist for saving trees must realize that forests represent the raw materials of business. The American Forest and Paper Association in a 2006 press release quoted Steve Rogel, head of the Weyerhaeuser pulp and paper company: “In the midst of tumultuous change, some things remain constant: Timberlands are the nucleus of this company, and our commitment to enhancing value for shareholders is as strong as ever.” But that same year, the nature advocate Ted Williams countered in Audubon magazine, “National forest timber has never been a major or (for the public at least) even a profitable resource. But 80 percent of the nation’s rivers originate in national forests, and 60 million Americans depend on national forest water.” Both Rogel and Williams expressed correct views: Forests supply a large portion of raw materials, but they also house a tremendous amount of biodiversity and nature as yet unspoiled by human activities.

A compromise on sustainable forest management that benefits both business and nature has yet to be found. Sustainable management decreases the rate of wood harvesting through various measures so that harvests can occur without decreasing the total forested land area. In some cases sustainable methods may even increase forest area. Agreement between environmentalists and the timber industry has grown slowly, with much work still ahead.

The World Resources Institute, based in Washington, D.C., has stated that analyzing the health of forests is complicated by four main factors. First, genetic diversity mapping is incomplete. Second, many tree species remain unknown. Third, science lacks a historical database on trends of forest growth and decline. Fourth, detailed monitoring is costly and time-consuming. A 2007 report titled State of the World’s Forests, published by the United Nations Food and Agriculture Organization (FAO), stated, “The biggest limitation for evaluating [conservation] progress is weak data. Relatively few countries have had recent or comprehensive forest inventories.” Therefore, lack of data hampers both staunch forest conservationists and forest harvesters when they try to meet their objectives.

In the United States, the U.S. Department of Agriculture’s (USDA’s) U.S. Forest Service serves as the federal agency in charge of overseeing the nation’s forest land. The Forest Service holds the dual responsibilities of conserving the land while at the same time serving people and industries that desire forests for recreation and profit, respectively. The Forest Service carries out the five following responsibilities: (1) manage the nation’s 155 national forests and 20 protected grasslands; (2) conduct scientific research; (3) reach out to state and private forests to coordinate fire management, disease control, and protections; (4) educate the public and schools on issues in forestry and forest conservation; and (5) develop cooperation with international agencies to formulate policies on forest management and protection. Forest Service Chief Abigail Kimbell said in 2008, “Kids must understand why forests are so valuable so they will grow into citizens who support conservation. Building on the Forest Service tradition of conservation education, we will work with partners t ensure that American children have the opportunity to experience the great outdoors, whether it is a remote mountain wilderness or a spot of nature in the heart of a city.” Like many aspects of environmental science, education of a new generation of conservationists will be critical for preserving the forests.

The Forest Service conducts research at experiment stations located in its nine regions and at the Forest Products Laboratory in Madison, Wisconsin. The experiment stations focus on disease, invasive species, soils, fire, native wildlife, forest monitoring methods, and the design of sustainable forests. The Forest Products Laboratory also specializes in research on the properties of wood and new directions for wood composite materials.

Many other national agencies and international organizations conduct activities similar to those at the U.S. Forest Service. The FAO compiles reports every three to four years that summarize the worldwide losses or gains in forests and the current conservation programs. One key factor that FAO monitors in regions of the world and globally is carbon stocks in biomass, which is the total organic matter produced by plants. The FAO’s State of the World’s Forests 2007 reported that from 1990 through 2005 carbon stocks rose slightly in North America and Europe, but plunged in tropical areas. Some areas increased their forest area, but most experienced decrease. Overall, therefore, forest management worldwide has not conserved forestland, and the global carbon stock decreased in those years 5.5 percent and lost 3 percent of its total forest area.

Seven current international agreements have a component for forest conservation, summarized in the table on page 25. Most of these agreements have been signed by the majority of the world’s countries.

Worldwide the FAO describes the success of forest management programs as “uneven.” Most countries must manage their forests for multiple uses. This means that certain countries with the best intentions of conserving their remaining forests, preserving biodiversity, and maintaining clean air, water, and soil believe they must destroy a portion of their forests to survive. Overall the world loses about 0.2 percent of forest every year. World forest management has yet to find a balance between attaining sustainable forest management and meeting the economic needs of all countries.

Forests serve people and animals as safe places of solitude and habitat far from the intrusion of urban life. Forests have long supported recreational activities such as hiking, horseback riding, camping, and swimming, while providing an important natural resource: wood fibers. For generations people have depended on wood for construction, furniture, paper, and heating fuel. The logging industry grew first on the East Coast of the United States as the population grew from the original colonies. Logging supplied the raw materials needed for the population’s westward expansion, especially in the hurried rush west after gold was discovered.

Today only 36 percent of the world’s forests are primary forests, forests that have never been disturbed by human activities on a large scale. In the United States, the U.S. Forest Service predicts that forest destruction will continue to increase to serve the country’s increased demand for wood and paper because of three factors: growing population, rising income levels, and upward economic activity. The U.S. Forest Service has estimated the country’s increased consumption of wood products based on 1986 figures through the year 2040, shown in the table on the next page. These figures take into account recycling programs, substitute materials, and efforts by the timber industry to enhance its efficiency.

The timber industry employs forest economics to determine the most inexpensive way to select, cut, and transport wood to the nearest mill. Today the timber industry must include plans for making harvests as efficient as possible in order to spare trees and to reduce wood waste.

Forest economics includes aspects of forestry that support sustainability in forest harvesting and regrowth. Some of the areas covered by forest economics target increased profitability of the timber business, and other areas focus on the development of sustainable forests. The main activities that contribute to forest economics are:

The conservation movement in the United States began to blossom in the early 19th century with the writings of James Fenimore Cooper, Ralph Waldo Emerson, Alexander von Humboldt, and Henry David Thoreau. Each shared a deep love and respect for nature and connected the conservation of nature with living a better life. One of the forest’s strongest advocates, John Muir, built upon the ideas of those writers and others when he developedhis views on nature, forests, and their spiritual value to people. Muir wrote in 1916, “Why should man value himself as more than a small part of the one great unit of creation?” Muir’s philosophy was to become known as the preservationist ethic, which valued nature for its intrinsic qualities. That is, nature has value whether humankind can derive a direct benefit from it or not.

Another key figure in the conservation movement was Gifford Pinchot, who became the first director of the U.S. Forest Service in 1905. Pinchot became interested in conservation as a young adult, but his education had relied on his father’s income from the timber industry. At about the same time that Muir formulated his theories on conservation, Pinchot proposed his own theory called the resource conservation ethic, which proposes that people view nature as a natural resource for their use. He stressed that this theory could work only if people used natural resources prudently to provide “the greatest good of the greatest number [of people] for the longest time.” Though Pinchot advocated making nature a commodity, he also made clear that natural resource management must serve not just the present but also future generations, so resources should be conserved and not wasted. In this way Gifford Pinchot may be said to have invented sustainable natural resource management.

The resource conservation ethic served the country well as it grew into a strong nation, despite the Great Depression in the early 1930s. Naturalist Aldo Leopold had agreed with Pinchot’s theory during his early education, but after graduating from Yale University in 1909, Leopold held less faith in the idea that nature existed only for man’s needs. In 1939 Leopold wrote in his essay “A Biotic View of the Land,” “. . . with one hand he [the biologist] points out the accumulated findings of his search for utility, or lack of utility, in this or that species; with the other he lifts the veil from a biota so complex, so conditioned by interwoven cooperations and competitions, that no man can say where utility begins or ends.” In his way, Leopold had described ecosystems and the intricate relationships among ecosystem members.

Aldo Leopold combined the early philosophies on nature with the resource conservation theory to develop the evolutionary-ecological land ethic, or simply the land ethic. The land ethic proposed that humans should be involved in land management but in a way that does not exploit the land or use up its resources. Leopold further envisioned conservationists making small improvements to nature to help biodiversity flourish. To this purpose, in 1935 Leopold teamed with two other environmentalists, Robert Marshall and Benton Mackaye, to form the Wilderness Society. The Wilderness Society today acts to protect unspoiled land while carrying out education, advocacy for the environment, and scientific studies.

Also in the 1930s, Franklin D. Roosevelt followed in the footsteps of his second cousin, Theodore Roosevelt. During Theodore Roosevelt’s two terms as president of the United States (1901–09) he led a strong push to make conservation a national priority. Theodore Roosevelt focused most of his conservation efforts on forests and wildlife, using the Forest Reserve Act of 1891 to set aside millions of acres of undisturbed land as wilderness. Almost all of the land Roosevelt protected was forest, mainly in the West and in Alaska. Franklin D. Roosevelt became president of the United States in 1933 after serving in the New York legislature as chairman of the Senate Committee on Forest, Fish, and Game. On the forests’ health at the time, he wrote, “. . . we are consuming five times as much timber as being grown. We plant in a year an area about equal to what is cut over in less than five days.” Two of Franklin Roosevelt’s landmark contributions to conservation were the Civilian Conservation Corps (CCC) and the Soil Conservation Service. History has shown that many of the projects conducted by the CCC led to environmental harm years later, but the notion of forests as important ecosystems was still a new idea. Roosevelt’s intentions were meaningful because they urged the American public to be responsible when managing the country’s natural resources.

Today conservation biology emphasizes forests and forest ecosystems. In addition to the Wilderness Society, other organizations raise funds or awareness in the public on the immediate need to halt further destruction of forests or have put concerted efforts into purchasing forest land to take it out of the hands of the timber and mining industries. The main organizations involved in protecting forests are listed in the appendix.

Though many people in the world understand that forests are threatened, factors in society sometimes override conservation. Economics represents a dangerous direct and indirect threat to forests. Subsistence communities need to find fuel, income, and food, and they often find these things in the jungle or forest. At the same time, industries want to continually grow and to do so they need ever-increasing amounts of natural resources. Along the way, the philosophy and the politics of forest conservation have taken some interesting turns. Two U.S. presidents in the past century demonstrate how divergent the world has become toward a simple tree.

“A grove of giant redwoods or sequoias should be kept just as we keep a great or beautiful cathedral.” Theodore Roosevelt made this statement in 1919 during a time in history when the country had not yet grown into a world leader in manufacturing. Horses pulled equipment over farmlands and carried logs out of the forest. Of course, U.S. commerce would emerge in the next 40 years, and presidents increasingly depended on backing from industrialists to win elections and make economic policy. President Ronald Reagan demonstrated a great shift in how nature could be viewed, particularly if preserving nature ran counter to making products and profits. In 1966 Reagan said in a speech to the Western Wood Producers Association, “I think, too, that we’ve got to recognize that where the preservation of a natural resource like the redwoods is concerned, that there is a common sense limit. I mean, if you looked at a hundred thousand acres or so of trees—you know, a tree is a tree, how many more do you need to look at?” Then as now, savvy politicians learned that keeping businesses happy might be just as important as keeping environmentalists happy. When leaders’ decisions regarding the environment are based on economics, however, the chances increase that natural resources will lose.

First, a disclaimer: Selling your organs is illegal in the United States. It’s also very dangerous. Handing off an organ is risky enough when done in a top hospital, even more so if you’re doing it for cash in a back alley. No, really: Don’t do this. OK? OK. There are many organs one can theoretically do without, or for which there’s a backup. Most folks can spare a kidney, a portion of their liver, a lung, some intestines, and an eyeball, and still live a long life. That said, donating a lung, a piece of liver or a section of intestines is a very complicated surgery, so it’s not done frequently on the black market. And no one’s going to make much cash on an eyeball. “In the U.S., there’s a fairly steady supply of donated corneas from corpses,” says Sean Fitzpatrick, director of public affairs at the New England Organ Bank. “There’s pretty much no market demand for eyes.”Giving up a kidney, though, is a relatively simple surgery that has netted desperate people a few bucks.

Now, black-market organ dealers don’t do a great job of filing taxes, but here are some prices based on rumored deals and reports from the World Heath Organization. In India, a kidney fetches around $20,000. In China, buyers will pay $40,000 or more. A good, healthy kidney from Israel goes for $160,000. Don’t expect to pocket all that dough, though. “The person giving up the organ only gets a fraction of the fee,” says Sally Satel, a scholar at the American Enterprise Institute think tank who studies the prices paid by legal and illegal organ-donor operations. After the organ broker—the guy who sets up your kidney-for-cash transaction—takes his cut, he needs to pay for travel, the surgeon, medical supplies and a few “look-the-other-way” payoffs. Most people get $1,000 to $10,000 for their kidney (probably much less than you were hoping for).

The best bet is to wait until compensation for organs is legalized in the U.S.—the Organ Trafficking Prohibition Act of 2009 would allow payment to donors, but it stalled in Congress—because there’s certainly a market for kidneys. Last summer, a man offering one of his for $100,000 (plus medical expenses) on Craigslist received several offers until the Web site removed his post. And you could probably hold out for even more. In 1999, before eBay delisted a kidney put up for auction, bidders drove the price up to $5.75 million.Source of Information : Popular Science February 2010

When TV went digital, Verizon, AT&T and other cellphone carriers shelled out a combined $19 billion for some of the freed-up airwaves, known as white spaces. Now wireless company Spectrum Bridge is using the parts that are still unclaimed to deliver highspeed Internet from its broadcast tower to your laptop computer. As soon as next month, the Federal Communications Commission is expected to allow commercial white-space Internet, which could help hook up the 54 percent of rural homes without broadband. These white-space channels use lower frequencies than Wi-Fi, so they can pass through physical obstacles easier and travel farther. Last October, Spectrum activated the first white-space network, in Claudville, Virginia, under an experimental FCC license. The town’s hilly landscape and abundant trees made conventional wireless near-impossible, so the company set up an Internet-connected radio transmitter at the town’s edge and gave the school, business district and a few homes modemlike radio receivers. “They’ve been trying to get connected to the outside world for the better part of this century,” says Jeff Schmidt, Spectrum’s director of engineering. Because wireless mics and news cameras can also use white-space channels, Spectrum’s system chooses among unused channels listed by the FCC. If all goes well in Claudville, the company plans to test the tech in the more crowded airwaves of cities this year.Source of Information : Popular Science February 2010

The International Maritime Organization, which oversees the shipping industry, will begin enforcing rules this July that mandate cleaner fuel to cut air pollution and acid rain. Ironically, this eco-motivated change will undo one of our strongest, if accidental, defenses against climate change. The regulations call for reducing the sulfur in shipping fuel—which is basically unrefined petroleum sludge—from 4.5 to 0.5 percent by 2020. Scientists project that this switch will cut sulfur-pollution-related premature deaths from 87,000 worldwide per year to 46,000. But the sulfate aerosols spewing from supertanker smokestacks also produce planet-cooling clouds called ship tracks, which form when water droplets coalesce around sulfate particles. These clouds, which are big enough to be seen from orbit, reflect sunlight back into space, preventing the equivalent of up to 40 percent of the warming caused by human-produced carbon dioxide. “The IMO has done a good job addressing air-quality issues,” says Daniel Lack, an atmospheric scientist at NOAA. “But there’s a climate impact that wasn’t necessarily considered.” Worse, the fuel switch won’t improve ships’ carbon emissions— if the industry were a country, it would be the sixth-largest CO2 emitter. The IMO plans to regulate CO2, but until then, it might be best to leave well enough alone.

Bacteria love hanging out between your teeth—food gets caught there, and brushing can’t reach all the germs. If the bugs settle in and form a cavity, your dentist must drill through your tooth just to get at it. But now dentists can trade their drills for a simple treatment that stops early-stage cavities. The Icon system lets dentists halt decay between teeth. Usually when a dentist spots an early cavity—when bacteria have eaten away enough tooth such that it’s a weak lattice but hasn’t yet degraded into a true cavity’s sinkhole—he prescribes an enamelstrengthening fluoride rinse and hopes the tooth heals itself. If that doesn’t work, the only option is drilling through healthy tooth to get to the problem spot. Icon, developed by dental-materials manufacturer DMG, does away with both the drill and the waiting time. A dentist simply slides a thin plastic applicator between the patient’s teeth and squirts the cavity with hydrochloric acid, which etches away the enamel to access the tooth’s deeper layers. Using a fresh applicator, he then injects a low-viscosity resin into the gaps in the tooth’s lattice and hardens the resin with a quick flash of high-energy blue light to fortify the tooth. DMG is working on a version that could hold up to the wear and tear of a tooth’s chewing surfaces, which company president George Wolfe hopes to have ready in a year. The sooner the better, he says: “One of my greatest fears is having to hold down my scared kid for a filling. Hopefully, I’ll never have to.”

In the face of all this bad news, what’s a calorie-compromised person to do? The best advice is to learn from the dangers of kamikaze dieting. Unless you’re morbidly obese (with a BMI over 40), don’t strive for the massive weight changes that get all the applause on Extreme Makeover. Instead, take the more cautious, careful approach outlined here:

• Have patience. Dramatic weight-loss is unsustainable. What’s the point in a twoyear plan for extreme weight loss if all you get is six months of skinniness? Instead, make lifestyle changes you can sustain forever. Focus first on preventing weight gain, and then aim to lose small amounts at a time. And don’t abandon your plan after one binging disaster. Instead, expect occasional setbacks and work through them.

• Instead of removing bad foods, add good ones. After all, if you take all the food that nutritionists have ever criticized out of your diet, you’ll be left with meals of Melba toast and oat bran (until the Atkins followers snatch that away from you, too). So concentrate on getting the benefit of good, nutritious food. Add one new healthy food a week, and before you know it, you’ll have crowded most of the bad stuff out of your stomach.

• Don’t invite extra calories into your home. To avoid binging on junk food, keep it out of your shopping cart in the first place. Once the food is in your house, the dynamic changes from “Why should I eat this?” to “I’m obviously going to eat this—why not now?”

• Keep eating the fat. Fat allows your body to build essential compounds and slows the digestion of your meal, helping you feel full. Cut out all the fat, and you’re likely to fill the void with something else—like a second serving of carbohydrates. Furthermore, the Nurses’ Health Study—a well-respected, longrunning study that tracks the health of over 100,000 nurses—suggests that there is no link between total fat consumed and heart disease, as long as you avoid the manufactured trans-fats found in many processed foods. This suggests that the fat on our bodies can’t blame the fat in our diet.

Let’s be honest. If you’re wrestling with weight, you’ve just read a lot of bad news, very bad news, and abjectly bad news. Basically, the problem is that your body doesn’t want you to lose large amounts of weight. It stubbornly clings to this point of view, even though science tells us slimming down would help it work better. Unfortunately, in battles like these, the body usually wins. But don’t give up just yet. If your weight is high or creeping up, you can’t afford to walk away from this battle. Here are some useful techniques:

• Copy successful losers. Surveys tell us that successful dieters—that rare breed of individuals who lose weight and keep it off—have a few characteristics in common. They look at their weight loss as a longterm lifestyle change, not as a quick fix. They exercise regularly, and their exercise combines calorie-burning aerobic exercise (like running, swimming, or dancing), with muscle-building weight training. But don’t be alarmed—there’s no need to haul out back-straining barbells or climb into expensive gym equipment. A few light weights can do wonders for your muscle tone and bone strength, boost your metabolism, and help fend off the ravages of age.

• Pretend to be skinny. Naturally thin people behave differently at the dinner table. They’re more likely to eat before they’re head-throbbingly hungry, and so they’re less likely to overeat. They eat slower and with less embarrassment. They’re picky, and they don’t clean their plates if the meal includes food they don’t really like or want. They also get up, move around, and fidget away dozens of extra calories a day.

• Become aware. Overeating is easy, if you don’t think about it. Unfortunately, a great number of people spend a great deal of time devising ways to encourage your automatic eating habits. (To learn about them, check out the eye-opening book, Mindless Eating). To put the thinking parts of your brain back in control, avoid eating while engaged in other activities (watching reality television, working on your taxes, and so on). Some dieters find that a food journal—a daily log of all the food they eat—forces them to face up to what’s on their plate. And one innovative study found that dieters who used a camera to take pictures of their every meal and snack were more likely to stick to their diets.

• Get a good night’s sleep. Skimping on sleep causes your body to release the stress hormone cortisol, which promotes fat accumulation. To be in fine form, insist on eight hours a night.

If you struggle with weight, none of these tactics will completely conquer excess pounds. But they will help you wrest a bit more control away from your body’s calorie-hoarding autopilot, and give you better odds in the never-ending battle against obesity.

When trying to control our weight, many of us try to adjust our eating first, often using a too-good-to-be-true fad diet. But as you’ve learned, eating is just part of your body’s complex weight-management system—and many of the other factors are out of your control.

If you’re a potential dieter, here are the facts you don’t want to know:• Most dieters succeed initially.

• Of those who do, very few keep their slimmed-down body weight for more than a couple of years. Most regain their original weight, along with a few extra pounds of anti-starvation insurance.

• Most dieters cannot lose large amounts of weight. As they reduce their food intake, the body slows its metabolism to compensate.

• Time is the great diet equalizer. Although some diets appear to work faster at first, the results are strikingly similar over the long term.

All of these points add up to a compelling reason not to diet—namely, diets rarely work. Unfortunately, a quirk of human biology makes diets appear to work better than they actually do, but only for the first few weeks. When you first reduce your eating, your body uses its storage of glycogen first. Glycogen is an energy reserve made up of sugar—it’s not as efficient as fat storage, so your body doesn’t keep a lot of it around. However, your body can get the energy from its glycogen reserve more easily, so that’s what it does. The trick is that glycogen can be stored only with a good bit of extra water. As you burn up the glycogen, your body releases the extra water. In other words, the easy initial weight loss of any new diet is usually excess water that your body will regain later. Fat is more persistent.

If all this isn’t bad enough, sudden weight loss may cause problems of its own, or at least fail to give you the health boost you expect. Here are the potential problems:

• When you lose large amounts of weight quickly, you’re likely to lose valuable muscle mass at the same time, especially if you aren’t performing a regimen of strength-training exercises.

• Some studies suggest that extreme dieting cuts out subcutaneous fat first, leaving the more dangerous visceral fat in place.

• Going through continuous cycles of weight loss and weight gain strains your body, and may encourage it to keep hoarding calories, making your weight creep up the scale.

Lastly, a body that’s been rapidly dieted down to a healthy BMI might not be healthy at all. Some controversial studies have discovered a phenomenon known as the obesity paradox. As you might expect, high BMIs are associated with higher rates of certain debilitating diseases (for example, congestive heart failure, coronary artery disease, and chronic renal disease). But the obesity paradox finds that once people have these diseases, those with higher BMIs have better survival rates. Some scientists believe this effect is just an illusion that might be caused by the fact that, at their more severe, many of these diseases can cause weight loss. But many experts argue that it reflects the danger of rapid weight-loss regimens, which can eat up healthy tissue from muscles and organs along with fat.

Most people are so familiar with the dangers of overeating that they never stop to think how odd it is that the human body can make such a colossal blunder. After all, the body is usually a miracle of self-regulation. Spend all day at the gym, and you still won’t end up with more muscle than you can carry around (unless you dose up on steroids). Shower every hour, and you still won’t end up with skin that’s six inches thick. But scarf a few dozen extra Twinkies, and you just might end up saddled with a sizable spare tire of fat. Clearly a better-designed body would compensate for this mistake by jettisoning extra calories. After all, few humans can use an extra 100-pound energy reserve. A more intelligent body would reach a set fat threshold and then stop accumulating any more. But the human body never developed this skill because it never found itself in this situation— until now.

Tens of thousands of years ago, it was critical that our ancestors ate every calorie that came their way. Obesity—the result of being able to find and eat vastly more of the nutrients that you need to survive in a harsh, physically demanding world—was virtually impossible. (In fact, it’s only in the last 50 years that scientists have collected worldwide obesity statistics—until then, obesity seemed like the relatively rare problem of a few compulsive eaters.) Your genes have been passed down from the most successful humans in those prehistoric days, and they had bodies that craved all the food they could get.

In other words, the sweeping timescale of evolution has honed your appetite-control system into a powerful force for preventing starvation—not for managing weight. If it’s any comfort, blame the cavemen. If they had found a way to eat themselves to diabetes and coronary heart disease 50,000 years ago, the forces of evolution would probably have solved the problem by now.

You’ve already learned how fat cells use lepti to talk to your brain, making it difficult to reduce your waistline without increasing your appetite. If that were the entire story, the science of food and dieting would be a tidy affair. Instead, the processes that regulate eating aren’t fully understood. They’re also multilayered, which means that your body uses multiple, redundant processes to get you to the dinner table. If something throws off the leptin signals, another system fills in to make sure you still feel hungry and get a good meal. This is one of the reasons that there’s no miracle pill for obesity on the way. When scientists attempt to tweak one set of hormones to promote light eating, the body adapts and chows down as steadily as ever.

Naturally Lean and Naturally FatThe discovery that different people harbor different numbers of fat cells hints at one of the unalterable truths about obesity. Some people struggle with weight their entire lives, while others wonder what all the fuss is about.

Truthfully, this shouldn’t come as a surprise. A long list of fascinating studies illuminates the strange workings of human fat storage. Here are some of the best:

• Starving the objectors. During World War II, more than a hundred men volunteered for a starvation study to avoid military service. Ancel Keys, a health researcher, took the 36 who were the most physically fit and psychologically healthy, cut their food intake to less than half, and put them on an intense walking regimen—similar to the punishing ordeals of the most hard-core dieter. The men lost a quarter of their weight over six months, and then were allowed to gain it back. During the dieting phase, they became obsessed with food, fantasizing about it for hours, collecting cooking implements, and scouring garbage cans. A few men broke the rules with sudden binging, after which they felt nauseated, depressed, and disgusted with themselves. And when they were allowed to choose their own meals again, many were no longer satisfied with normal portions, and ate insatiably. All of these details sound like a natural response to extreme circumstances—but they also have an uncanny similarity to the experiences of crash dieters.

• Feeding the prisoners. Another study took the opposite approach. Ethan Sims started with normal-weight volunteers from a state prison, and deliberately overfed and underexercised them until they grew fat. Much to everyone’s surprise, fattening people up was nearly as challenging as slimming them down. Different prisoners needed different amounts of excess calories to gain weight, but most of them required huge amounts of food to gain a significant amount of extra weight. At the end of the study, the prisoners effortlessly returned to their original weights—again at varying, self-determined rates.

• Comparing twins. It’s no surprise that people with obese parents are more likely to be obese themselves. There are a range of possible explanations, including poor dietary habits and bad role models. But more intriguing studies examine adopted children and identical twins who were raised in separate families. These studies found that fatness has a powerful genetic link—in other words, children are likely to drift toward the body mass of their birth parents, even if they’ve never met them.

Faced with this evidence, it’s natural to wonder what some people have done to deserve the short (and fat) end of the genetic stick. The oftenrepeated line that skinny people have fast metabolisms doesn’t seem to be true. Instead, people of all body weights maintain the same weight through most of their lives, eating an appropriate amount for their size. However, when people are pushed out of that range with forced starvation or overfeeding, the body fights back, making meaningful, long-term weight change extraordinarily difficult. This doesn’t mean that a fat person can’t get thin, but it certainly changes the rules of the game.

For popular accounts of fat research, check out these two slim books: The Hungry Gene (Ellen Ruppel Shell) explores the science and business of obesity research. Rethinking Thin (Gina Kolata) covers some of the same ground, while following a group of dieters in a weight-loss study who have big dreams but are destined to come up short.

Since the 1990s, Costa Rica has been the site of one of the world’s most ambitious ecological restoration projects. Ecological restoration is the act of altering a habitat in order to return as much of it as possible to its original state. In the 1990s Costa Rica’s Tropical Forestry Initiative purchased 350 acres (1.4 km2) of land that had been cleared and used for ranching for the next 50 years. The initiative sought to restore a tropical wet forest (one receiving more than 100 inches [254 cm] of rainfall yearly) on the abandoned pastureland by planting 40,000 seedlings of a mix of 35 native tree species. One such preserve, named Los Arboles, will require from 100 to 800 years for the forest to mature, so the experiment remains in its earliest stages. Ecological restoration usually cannot restore all the native species by reintroducing them to an area, so in Los Arboles the best hopes are centered on a plan to nurture the planted seedlings and accelerate the growth of as many native species as possible. In order for restoration like Los Arboles to succeed, four important steps must occur: growth of the seedlings; dispersal of new seeds; germination of seeds; and avoidance of predation. Soil depleted of nutrients or areas with little available water increase the difficulty of restoring any forest.

A variety of techniques have been used in Costa Rica to assist natural processes in forest recovery. Forest restoration depends on seed dispersal by insects, rodents, and birds that eat seeds and eliminate undigested seeds in their waste in a new location. Restoration teams now help this process in two ways: by growing a healthy shrub understory and by providing perches for birds. Shrub understories provide habitat to attract birds, rodents, and insects, replenish soil, and keep aggressive grasses from hindering the growth of seedlings. Costa Rica’s young seedling trees needed time to reach a size suitable for perching of seed-dispersing birds, so workers built artificial perches. Other methods serve the same purpose as man-made perches. For instance, workers can plant young woody trees on the restoration’s perimeter to give birds a place to find shelter and roost. On restored rangelands, ranchers often leave a few stands of trees to provide shade for their cattle. These well-established trees already house insect and bird populations acclimated to the area, so they, too, aid the restoration.

In the northern part of Costa Rica, the biologist Daniel Janzen of the University of Pennsylvania has led a second restoration project in the tropical dry forest (which contains a distinct dry season) in Guanacaste National Park. Janzen and his students developed seedlings of the area’s native trees in his laboratory, then organized field trips from the United States to sow the seeds and plant seedlings. From the start Janzen included local students and farmers so that they could learn the restoration techniques. Since the local people participate in the recovery of their own natural resources for their long-term benefit, Guanacaste presents an example of biocultural restoration. This means both the environment and the local population receive some sort of recovery. In the community’s case, the residents received greater opportunity for earning higher income. Eventually, Costa Ricans will run the park with no outside influence.

Ecologists measure the progress of restoration by monitoring increases in number and diversity of species moving into the new habitat. Within the first decade of new growth in Costa Rica, woody plants and a diverse mixture of mammals, birds, and invertebrates began building populations. The Tropical Forestry Initiative recorded tree growth and species, finding that many trees grew 7.2 feet (2.2 m) per year and a canopy developed five years after planting seedlings. In addition, researchers counted more than 350 plant species that had become established in the new forest.

Restoration ecology would probably not be successful if left entirely to humans or entirely to nature, but the projects in Costa Rica prove they can work in tandem. Janzen described it this way in an essay he wrote for Science in 1998: “Why can’t the wild tropical species be left ‘out in the wild’ to fend for themselves? Because the wild is at humanity’s mercy. Humanity now owns life on Earth. . . . Until the Pleistocene, not more than a few thousandths of 1 percent of the Earth’s surface was ours. Today it all is. If we place those species anywhere other than in a human safe zone, they will continue in their downward spiral as grist in the human mill, just as they have for the past 10,000 years.” Though restoration ecology manipulates nature, it profits nature in the long term.

The Los Arboles project also relies on the success of its biocultural restoration activities. In 1997, David Knowles and A. Carl Leopold of the Tropical Forestry Initiative said in an ecology presentation, “A crucial part of this effort will be to spark interest among the local landowners. We are working with local landowners to encourage reforestation by providing them with seedlings, by participation in a local forestry association, and by interacting with local schools.” More than decade later, both of these forest restoration projects have engaged the local communities in the areas of restoration, ecotourism, and environmental education.

Forests support biodiversity through indirect means by helping water and soil conservation and climate regulation. Directly, forests provide habitat for about two-thirds of all species on Earth, and by so doing forests may be the single most important constituent in maintaining the Earth’s biodiversity. Forests support not only diverse animal species, small plants, and microbes, but forests also contain diverse mixtures of different trees that grow and recycle nutrients at different rates and provide biomass of varying compositions when the trees die.

In the United States, land designated as protected national forest covers 192 million acres (78 million km2). These forests contain almost every habitat in the country: tropical and temperate rain forests, coasts, rivers and lakes, grasslands, mountain and alpine areas, deciduous forests, conifer and mixed forests, old-growth forests, arctic tundra, deserts, and wetlands. National forestland gives habitat to at least one-third of all wildlife on the endangered species list. Rich biodiversity within any forest serves as an indicator of the health of that forest; the greater the diversity of plants, animals, and microbes, the healthier the forest.

Forests support biodiversity in a horizontal fashion as well as a vertical fashion. Horizontal forest growth refers to the forested land across continents, which provide different climates and terrain. This is the core reason why tropical rain forests at the Earth’s equator bear little resemblance to evergreen forests in Canada. Each forest possesses its unique biodiversity, and this diversity contributes hundreds of different types of habitats for animals, plants, and microbes. Vertical biodiversity in forests resides from the upper part of the tree line, the canopy, to the roots in the earth. From top to bottom, a single forest can house ecosystems containing raptors, seed- or insect-eating birds, tree-dwelling mammals, insects and snakes that live lower on trees, small rodents and plants on the ground, and invertebrates and microbes digesting biomass within the soil. This model describes merely a general look at the forest ecosystem; forest food webs contain many more complex animal-plant-microbe relationships within each different type of forest.

The world’s biodiversity concentrates in tropical rain forests, which cover only 7 percent of the Earth’s land, but hold at least 50 percent of all the Earth’s species. For this reason the tropical rain forests in many parts of the world have been designated biodiversity hot spots by Conservation International. Environmental expert Norman Myers first proposed the concept of biodiversity hotspots in 1988 to describe places that contain a high degree of biodiversity and are simultaneously under a high threat of being destroyed. In that year Myers wrote an essay titled “Tropical Forests and Their Species” stating, “Extinction has been a fact of life since the emergence of species almost four billion years ago. . . . Whereas past extinctions have occurred by virtue of natural processes, today the virtually exclusive cause is Homo sapiens, who eliminates entire habitats and complete communities of species in super-short order. It is all happening in the twinkling of an evolutionary eye.” Though Myers spent his career addressing both plant and animal diversity, his words can certainly be applied to the plight of forest loss taking place today.

Deforestation refers to any removal of trees from a forested area without adequate replanting, and it represents the biggest threat to tropical rain forests and the species dependent on them. Many of these forests are in areas with high population growth rates compared with the rest of the world. In general, a large area of the world’s tropical rain forests have fallen victim to population growth, poverty, and inadequate government protection. These are not simple matters to overcome when trying to design plans for protecting trees. The case study “Conservation in Costa Rica” provides a look into one ambitious forest recovery program.

A forest canopy consists of the area above the forest floor where tree crowns containing branches and leaves meet. At 200 feet (61 m) or more above the ground, the canopy performs more than 90 percent of a forest’s total photosynthesis because it is the portion most exposed to sunlight. For that reason the canopy stores 60 percent or more of the Earth’s carbon while supporting a food web that is more diverse than any other. Carbohydrates made in photosynthesis provide the foundation for food webs that live solely in the canopy and also for ecosystems that extend to the forest floor.

Tropical, temperate, and boreal forests each have their own unique canopies, but there are basic similarities among them. The canopy’s overstory contains towering trees spaced closely together so their branches and leaves form a continuous community. The understory consists of more widely spaced shorter and juvenile trees. Because forests across the globe receive different amounts of sunlight, water, and wind (or storms), the various canopies affect the organisms living nearer the forest floor differently. For example, the canopy of coniferous forests filters light through narrow leaves, allowing organisms living in the canopy and below to receive small amounts of direct sunlight. Broadleaf tree canopies, by contrast, block the sunlight and provide a dark and moist environment below.

In addition to filtering sunlight and performing photosynthesis, the forest canopy provides five services to the environment: nutrient delivery to the soil in the form of biomass, when leaves and small branches fall to the forest floor; soil erosion reduction by protecting the ground from heavy rainfalls; particle and pollutant removal from the air, rain, and fog; transpiration in the water cycle; and habitat for animal and plant life that exist only in this place. The canopy habitat is so specialized, in fact, that it makes up what is known as a microhabitat. A microhabitat is an area within a larger habitat that has unique characteristics found nowhere else in the environment.

Plants that live only in the forest canopy are epiphytic plants, meaning they receive physical support from the canopy and not by putting roots into soil, and they draw water and nutrients directly from the atmosphere. Epiphytes contain about 30,000 species, including Spanish moss, lichens, liverworts, ferns, cacti, vines, and up to 70 percent of all orchids.

The canopy’s animal life is also unusual because the canopy includes species that rarely if ever visit the ground. A wide variety of flying and crawling insects, including bark-eating and wood-boring insects and spiders, mites, centipedes, and millipedes, live in the canopy. Invertebrates such as worms, snails, and slugs also live as either carnivores or herbivores in addition to the reptiles and amphibians that are found there. Songbirds and woodpeckers spend entire lifetimes in the canopy, and raptors such as hawks and owls hunt from the canopy. Some 90 percent of all tropical rain forest organisms stay in the canopy their entire lives.

Warm-blooded life in the canopies of the world, especially in tropical rain forests, is the most diverse on Earth. Monkeys and lemurs have prehensile tails that enable them to grab branches, while other animals evolved as gliders to travel through the forest’s upper reaches. Flying squirrels, colugos, Draco lizards, and flying frogs possess a body form that catches the air and helps them glide from branch to branch. The slowmoving sloth also lives exclusively in the tropical rain forest canopy by clinging to tree trunks with sharp claws.

Urban areas have started taking a cue from nature by planting trees in treeless neighborhoods, partly because of the benefits of the canopy. Urban tree canopies help reduce city carbon dioxide levels and pollutants, absorb storm water, provide shade to decrease the use of air conditioners, and reduce traffic noise. Very often, trees in the city increase property values. Said Kelly Quirke, head of Friends of the Urban Forest in San Francisco, California, “As more of us live in cities and as we lose more open space, people are getting more and more of their experience in nature in their urban environment. That means the urban forest becomes ever more critical.” An urban forest can never replace the unbroken expanses of forestland that existed before towns grew up, but they make their own contribution to returning some habitat to large metropolitan centers.

The water cycle, also called the hydrologic cycle, operates similarly to biogeochemical cycles in which plant and animal nutrients move through the atmosphere, the earth, and through living things. The water cycle includes water in the forms of solid, liquid, and gas, and the Sun provides the energy needed to power the constant cycle of water among these three forms. The water cycle occurs in oceans, bays, lakes, ponds, rivers, and streams. The ocean covers most of the Earth’s surface and so contributes the largest share to the water cycle; more than 85 percent of the water that evaporates from the Earth’s surface into the atmosphere does so from the ocean. About 80 percent of the world’s precipitation enters oceans.

The water cycle contains five components that transfer moisture either from the Earth’s surface to the atmosphere or from the atmosphere back to Earth. These components are the following:

• condensation—conversion of water vapor into droplets of liquid water

• precipitation—water that falls from the atmosphere to land or to surface waters as rain, snow, sleet, or hail

• infiltration—downward movement of liquid water through soil

• evaporation—conversion of liquid water into gas, or water vapor

• transpiration—movement of liquid water from plant roots, upward in vessels, and into the atmosphere from the leaves as water vapor

Forests serve in the water cycle in two critical ways: transpiration and water storage. Both animals and plants transpire water vapor into the air, but animals transpire as part of aerobic respiration when they exhale moisture from their lungs. Plants and trees possess special cells on the underside of their leaves, called guard cells, that release water vapor from the plant into the atmosphere. The transpiration process begins when trees draw water from the soil through their roots and transport it upward in vessels—xylem carries water and nutrients upward, phloem distributes water and nutrients throughout the plant. Trees, depending on size and species, transpire from 5,000 gallons (18,921 l) to almost 50,000 gallons (189,210 l) of water per year, more in warmer weather and less in colder weather. Low relative humidity and increased air movement caused by wind or breezes also increase the transpiration rate. During drought or in the desert where only drought-tolerant plant life lives, a tree’s transpiration rate decreases so that it can conserve water. Soil also affects water transpiration. When soil moisture levels are low, as in drought, trees slow their transpiration rate to conserve water. Trees undergoing the normal aging process, called senescence, give way to new trees ready to take their place. Prolonged drought, however, puts all trees into a premature senescence, an event that may eventually kill a forest. Global warming has exerted a critical effect on forest health because it increases the incidence and severity of droughts worldwide, and in doing so it accelerates the death of drought-vulnerable trees.

Forests’ second major activity involves the capacity of trees to store water. Trees act as a watershed by absorbing water during floods and storing and slowly releasing water in times of low rainfall. Surface waters, groundwaters (or aquifers), and plant life comprise the Earth’s total watershed. Part of trees’ role in the watershed involves regulation of the water table, which is the area underground where water has completely filled the spaces between rocks and soil particles. Beneath the water table lies an area of higher density where all the air has been squeezed out to make room for water. This location, called the zone of saturation, holds water undisturbed for longer periods than the water table. Therefore, water moves through three layers in the earth: the upper unsaturated zone, where soils hold varying amounts of moisture (also called the soil zone); the water table, where water exchanges from the saturated layer below to the unsaturated layer above; and the zone of saturation. Tree roots pull water from either the unsaturated zone or the water table.

Human activities interfere with the water cycle in the three following ways: by drawing large amounts from surface sources and groundwaters, by polluting water, and by removing or damaging the world’s forests. Part of the problem of water use by the Earth’s human population resides in the fact that water is a very poorly managed resource. Water covers 71 percent of the Earth and makes up at least 60 percent of living cells, but only 0.014 percent is available for people’s use. Yet humans continue to waste water, pollute it, or otherwise treat it as if it were free. Benjamin Franklin once said, “When the well’s dry, we know the worth of water.” The world has been progressing toward ever greater water shortages since the acceleration of global warming. Some countries have already entered a dangerous condition known as water stress, meaning their water requirements exceed the water they have available.

Since every living thing needs water and cannot exist without it for more than a few days, maintaining a clean supply is paramount to maintaining biodiversity. Forests play a vital role in maintaining a continuous supply of available water, so this represents one way in which forests maintain biodiversity. As the next section and the sidebar “The Forest Canopy” point out, forests add to the world’s biodiversity in other immeasurable ways.

The Sun’s energy powers the water cycle, which is critical for conserving Earth’s water. Within this cycle, oceans account for more than 80 percent of evaporation, and more than 80 percent of rainfall lands in the oceans.

Groundwater serves as a major source of drinking water in most of the world, but high water demand due to growing populations draws down the reserves, lowering the water table. Pollution further threatens groundwater reserves. Metals, pesticides, and organic chemicals have infiltrated many once pristine aquifers.

Forests exist on almost every part of the globe’s land. Forest complexity causes scientists to classify forests in more than one way, by location, the type of wood they produce, or their age. Sometimes these three classifications interconnect. Ecology uses a forest classification system based on climate, determined by precipitation and temperature. This classification system correlates to where on the globe the forests grow. Each of the three main classifications contain subcategories based on more detailed climatic conditions: tropical, subtropical, Mediterranean, temperate, coniferous, boreal, and montane (cloud forest). Some of these groups contain additional subtypes.

Forests also belong to categories according to the types of trees that predominate; for example, coniferous, mixed broadleaf, aspen, oak, or mangrove forest. Finally, forest age determines characteristics of this habitat, so forests may be identified as immature, secondary, primary, or old-growth.

The World Resources Institute’s Global Forest Watch program states on its Web site that the Earth has lost almost 50 percent of its forests in the last 8,000 years, the same time period in which civilization developed. The highest rates of today’s forest loss occur in Africa and South America; every five years Africa and South America lose 3.2 and 2.5 percent, respectively. These numbers can be deceptive because in some African nations the combined grassland and forest loss tops a rate of 10 percent annually. Grasslands have in fact undergone more drastic reductions than forests in some places, particularly Africa. If these current disappearance rates continue, many countries will lose all their forests within a few decades.

Forest loss has a devastating impact on biodiversity because forests, especially the tropical rain forests near the equator, make a great contribution to the world’s plant and animal diversity. These tropical rain forests account for at least half of all the Earth’s biodiversity even though they cover only about 2 percent of the Earth’s surface. These forests have also become the most threatened by deforestation.

Deforestation refers to any removal of trees without replacement, and it threatens forests in direct and indirect ways. Direct deforestation comes from four main causes: clearing of tropical forests for crops, livestock, and timber; clearing of temperate deciduous forests for timber, crops, and urban development; clearing of evergreen coniferous forests for timber; and conversion of forests to monoculture (vineyards, commercial tree farms). Illegal logging makes up part of the deforestation problem, much as exotic animal poaching decimates protected wildlife populations. Logging is the process of cutting and removing logs from the forest.

Indirect causes affect forests similarly to how they affect animal species. Three important indirect threats to forests are roads, climate change, and habitat fragmentation. Indirectly, off-road vehicles used to build roads damage seedlings and new growth, increase soil erosion, and fragment habitat. Climate change affects environment by shifting the optimal temperature range in habitats. Wildlife can migrate to a different elevation or latitude to find the ideal temperature. Trees, however, do not possess the luxury of moving; entire species can slowly die as a result of continuous temperature changes. Climate change also makes conditions suitable for invasive species to enter a habitat and may additionally open the door to increased incidence of disease or pest infestation. Habitat fragmentation from urban growth or agriculture reduces the ability of tree populations to propagate and lessens their genetic diversity.

All of these effects caused the world to lose 3 percent of its forests in a 15-year period from 1990 to 2005, a rate of 0.2 percent a year. At present, the world’s forested areas continue to decrease but the disappearance rate has been slowing; Europe and North America have now reversed centuries of forest loss. The most threatened forests reside in Africa, Latin America, and the Caribbean. Fortunately, national governments in Africa have started cooperative programs for forest conservation, and individual nations have adapted new forest policies and forest laws. New forestry management programs help save forests to some extent, but fires, regional conflicts, and legal and illegal industries have continued the deforestation crisis. The table on the next page provides details on today’s major threats to forests and their primary location, though all of these threats can be found to some degree in almost every part of the world.

Many people may assume forest fires pose the greatest threat to forests. In the United States, the Smokey Bear campaign began in the 1940s to remind people of the dangers of forest fires. Illegal campsite fires, arson, and blazes cause damage each year in dry areas of the United States that have dense human populations. But fires in general, natural or human-caused, do not threaten the overall population of forests, and fire management makes up an important sector of overall forest management. Fires actually contribute to the health of forests and plant communities by• enhancing nutrient recycling• allowing for small plants to spread• regulating the succession of new tree growth• developing new habitat• reducing biomass buildup• enriching soils• reducing parasites and disease-causing organisms

In North America and Europe, forestry programs work in conjunction with the government. The success of slowing forest loss in these places varies, however. Forest area stabilized in Canada and the United States in the mid-2000s, but forest area continues to shrink in Mexico, although fortunately the rate has slowed. In Europe, lands set aside for protected forests have increased slightly in the past five to 10 years. Asia and the Pacific have halted an alarming trend of forest loss that took place during the past 30 years, and in these places forested land may now be increasing in area. However, part of East Asia’s statistics may be misleading. China has planted large forest plantations, and while these plantations add to the total amount of land that forests cover, such monocultures do little to improve biodiversity.

Trees in the forest interact with other living things in ecosystems just as plants, animals, and microbes do. An imbalanced ecosystem can therefore harm trees. For example, if a predator were to disappear, other animals may grow to higher population numbers and graze all the young seedlings needed to regenerate the forest in 100 years. An alteration to a plant community in the forest likely alters the birds and reptiles living there, which can affect populations of tree pests and parasites. Trees weakened by a parasite become more vulnerable to infection by disease-causing microbes.

Climate change holds paramount importance in forest health because it affects seasons, normal temperature ranges, and tree reproduction. Climate change has also influenced the world’s availability of clean water. Like all living things, trees cannot survive long without water, but equally important, trees play a crucial role in the Earth’s water cycle.

If all this sounds colossally unfair, well, it is. But even if the genetic deck is stacked against you, you’d probably escape unharmed were it not for the cooperation of a seriously skewed environment.

After all, obesity is a recent phenomenon—so recent that worldwide obesity statistics stretch back less than a generation. In the wild, virtually no other species experiences true obesity. Not only do humans break the mold, we also have the dubious distinction of being the only species to bring obesity to other animals, such as our overfed pets, livestock, zoo dwellers, and experimental subjects.

So what’s gone wrong in our world to shift a huge number of people— the majority in many countries—into excessive weight? Although there’s no definitive answer, it seems overwhelmingly likely that a set of factors work together to help make us fat. The following sections explain what they are.

Changes in activityFor tens of thousands of years, humans spent the better part of the day in activities we’d call exercise, with only the occasional period of rest. Today, the balance has neatly flipped, and our bodies are left sitting around like an idling automobile engine for most of the day.

Changes in foodAt the same time that we’ve switched from lives of restless activity to permanent relaxation, we’ve changed the way we fuel our bodies. Generations ago, we had no choice but to fill up with natural, unrefined foods that took a fair bit of digestive effort to convert to energy (and fat). By comparison, even the healthy eaters of today down huge quantities of processed, highcalorie, high-carbohydrate foods, which contain enough energy for an Olympic rowing team.

The breakdown of food cultureStudies show that people who eat a diet traditional to their native culture fare better than average eaters. This is true whether the culinary tradition is Greek, Italian, Japanese, French, or something else—even though all these diets are dramatically different and many emphasize sometimes stigmatized foods like pasta, rice, fatty meat, or butter.

There are two possible explanations. One is that the diet most Westerners eat—heavy on processed convenience foods—is, biologically speaking, the worst possible rubbish we could use to fuel ourselves. The other possibility is that people who are part of a traditional food culture are also guided by firm, unwritten rules that govern acceptable eating practices.

For example, consider the so-called French paradox—the fact that French people have a relatively low incidence of heart disease, despite enjoying a diet rich in cheese, cream, and other sources of saturated fat. Unlike North Americans, French eaters are part of a dining culture that emphasizes slow, shared meals. It discourages second helpings and snacking. And if you think you’ve got it bad, consider the plight of cultures that have moved from ancient cuisine to Western convenience foods in a single generation. Two examples are the desert-dwelling Pima Indians and the settlers of the tiny Micronesian island of Kosrae. Both populations are small, genetically similar, and cut off from the rest of the world. For generations, they lived through periods of intermittent famine that were more severe than those faced by most Europeans. Today, they’ve adopted a Western diet and suffer from staggering rates of obesity and diabetes, far worse than the rest of modern society. Scientists are still battling over whether the problem is environmental (for example, the population is particularly susceptible to Western conveniences because their old way of living and eating is obsolete) or genetic (perhaps they have a higher incidence of genes that spur overeating).

Environmental programmingIt’s a bit speculative, but many obesity researchers believe environmental cues during pregnancy or childhood activate certain genes in the body, putting a process in motion that ultimately leads to adult obesity. It’s not a far stretch—after all, not only have people been fattening up generation after generation, they’ve also been growing much taller and reaching sexual maturity far sooner. In studies of strains of obese rats, a brief period of underfeeding in infancy reduces their fatness in adulthood. A similar diet in later life has only temporary effects.

The discovery that different people harbor different numbers of fat cells hints at one of the unalterable truths about obesity. Some people struggle with weight their entire lives, while others wonder what all the fuss is about. Truthfully, this shouldn’t come as a surprise. A long list of fascinating studies illuminates the strange workings of human fat storage. Here are some of the best:

• Starving the objectors. During World War II, more than a hundred men volunteered for a starvation study to avoid military service. Ancel Keys, a health researcher, took the 36 who were the most physically fit and psychologically healthy, cut their food intake to less than half, and put them on an intense walking regimen—similar to the punishing ordeals of the most hard-core dieter. The men lost a quarter of their weight over six months, and then were allowed to gain it back. During the dieting phase, they became obsessed with food, fantasizing about it for hours, collecting cooking implements, and scouring garbage cans. A few men broke the rules with sudden binging, after which they felt nauseated, depressed, and disgusted with themselves. And when they were allowed to choose their own meals again, many were no longer satisfied with normal portions, and ate insatiably. All of these details sound like a natural response to extreme circumstances—but they also have an uncanny similarity to the experiences of crash dieters.

• Feeding the prisoners. Another study took the opposite approach. Ethan Sims started with normal-weight volunteers from a state prison, and deliberately overfed and underexercised them until they grew fat. Much to everyone’s surprise, fattening people up was nearly as challenging as slimming them down. Different prisoners needed different amounts of excess calories to gain weight, but most of them required huge amounts of food to gain a significant amount of extra weight. At the end of the study, the prisoners effortlessly returned to their original weights—again at varying, self-determined rates.

• Comparing twins. It’s no surprise that people with obese parents are more likely to be obese themselves. There are a range of possible explanations, including poor dietary habits and bad role models. But more intriguing studies examine adopted children and identical twins who were raised in separate families. These studies found that fatness has a powerful genetic link—in other words, children are likely to drift toward the body mass of their birth parents, even if they’ve never met them.

Faced with this evidence, it’s natural to wonder what some people have done to deserve the short (and fat) end of the genetic stick. The oftenrepeated line that skinny people have fast metabolisms doesn’t seem to be true. Instead, people of all body weights maintain the same weight through most of their lives, eating an appropriate amount for their size. However, when people are pushed out of that range with forced starvation or overfeeding, the body fights back, making meaningful, long-term weight change extraordinarily difficult. This doesn’t mean that a fat person can’t get thin, but it certainly changes the rules of the game.

For popular accounts of fat research, check out these two slim books: The Hungry Gene (Ellen Ruppel Shell) explores the science and business of obesity research. Rethinking Thin (Gina Kolata) covers some of the same ground, while following a group of dieters in a weight-loss study who have big dreams but are destined to come up short.

It’s every string bean’s worst nightmare: What if natural, effortless skinniness isn’t the hallmark of health, but a socially acceptable veneer hiding some of the same health problems?

If this idea troubles you, thank Dr. Jimmy Bell, a British scientist who has scanned more than 800 people with MRI machines to study their fat. One of his most disquieting discoveries was that nearly half of people with normal-weight BMI scores actually had excessive amounts of visceral fat buried inside their bodies. Apparently, those most at risk for hidden visceral fat are people who seldom exercise and maintain their weight through diet alone. As Dr. Bell puts it, “Being thin doesn’t automatically mean you’re not fat.”

While this should worry the skinny, it isn’t much comfort to the obese. They’re even more likely to have still larger deposits of visceral fat. The only exception is if they’re extremely athletic. For example, some studies suggest that sumo wrestlers, despite their proudly displayed subcutaneous fat, actually have a fair bit of muscle and surprisingly little visceral fat.

Dr. Bell’s discoveries are controversial, and they call into question virtually everything we say about fat. After all, if you can have health-damaging amounts of fat without being fat, how can anyone really get a handle on the danger of these dastardly cells?

Now you know about visceral fat—the greasy matter that’s buried deep inside your abdominal cavity, packed around your internal organs, and up to no good at all. The obvious question is this: What can you do to get rid of this accursed stuff?

Although the science isn’t settled, several studies suggest that dieting might be less helpful than you think. The problem is that it’s likely to shrink your subcutaneous fat without reducing the dreaded deposits of visceral fat that lurk inside. Instead, you need to add high-intensity exercise to the mix (say, 30 minutes of pulse-racing activity, four times a week) to pare down visceral fat. Some experts believe that even happily thin people can have hidden deposits of visceral fat (see the box on this page) and need the same exercise regimen to stay healthy.

There’s one practice that definitely won’t help: liposuction. Although getting the fat vacuumed out of you seems like a fiendishly convenient shortcut, liposuction sucks up subcutaneous fat only. This is probably why it has no long-term health benefit. Studies show that happily liposuctioned people don’t do any better on key measures of health and inflammation (including the blood tests listed on page 49) than others. This is true even when massive quantities of fat are removed—in one study, 20 pounds at a time.

So far, there’s no way to liposuction away your visceral fat. However, small experimental studies have found ways to surgically remove it. In one study, visceral fat was removed from a group of obese men with insulin resistance, the precursor to diabetes. Even though they stayed obese, with copious amounts of subcutaneous fat, almost all of them lost their insulin resistance within a year.

Source of Information : Oreilly - Your Body Missing Manual

Think health gain, not weight loss. Most people find it easier to concentrate on doing something good than on trying to stop something that’s gone wrong— especially if you shoulder hefty feelings of guilt for the pounds you’ve already put on. So make fitness your goal, and use weight loss and exercise as just two of your tactics to get healthy.

You probably already have an inkling about where your body stores its fat. But if you’re overweight, it’s important to know how much of your excess padding consists of hazardous visceral fat. To get the final word, you’d need to scan an image of your body with a high-priced MRI machine. But even if you don’t have any hospital equipment in your basement, you can still look for a few clues, such as your belly width and body shape:

• Apple-shaped bodies have more fat around the abdomen and the chest.

• Pear-shaped bodies hold a lot of their extra fat on the outside—primarily around the thighs and bottom.

Although apple-shaped bodies have their share of subcutaneous fat, they’re more likely to store dangerous quantities of visceral fat. This makes sense if you remember where your body stores visceral fat—in the space around your abdominal cavity. As visceral fat plumps up, it pushes the rest of your body out, creating the distinctive apple shape. The following MRI scan reveals the inner world of fat.

Everyone has subcutaneous and visceral fat, no matter what their body type. Although the apple body shape is a warning flag, pears aren’t necessarily safe. Another worthwhile check for visceral fat is to measure your waist. If you’re a woman with a waist that measures 35 inches or more, or a man with a waist that’s 40 inches or more, you have a significantly higher risk for diabetes and heart disease.

Your body has plenty of hiding places to stash fat. Where fat goes is completely beyond your control—it depends on your gender, age, and genetic inheritance. But here’s the unfair part: even though you can’t choose where your body stores its fat, those locations can have serious consequences for your health. Studies show that the risks of excess fat increase dramatically when it’s stored in certain places.

Essentially, there are two basic storage zones for your fat:

• Subcutaneous fat. This fat is stored in a layer around your body, just under your skin. Once again, genetics determine where the padding is thickest. In women, common storage depots include the thighs and posterior. In men, fat is more likely to hang out around the abdomen. Subcutaneous fat is also responsible for cute baby faces and the dreaded cellulite (lumpy deposits of fat that cause a dimpled appearance in skin, usually in women).

• Visceral fat. This fat is buried under your muscles, deep inside your body. It pads the space around your internal organs. Most experts believe visceral fat is far more dangerous than subcutaneous fat, and leads to a higher risk of heart disease and diabetes.

Subcutaneous fat is by far the more popular fat parking zone, accounting for the majority of fat in anyone’s body. Smaller quantities of fat can also end up stored in your muscles (where it’s called intramuscular fat) and inside certain organs (such as the liver), where it’s especially dangerous.

There’s no consensus on why visceral fat is the fat to fear. It’s possible that the hormones it releases interfere with the functioning of nearby organs or compels them to start storing their own fat reserves, which can cause further damage.

No matter what foods you eat or exercise you practice, you can’t remove fat from a specific part of your body. In fact, studies have shown again and again that spot reduction is impossible. Lifting weights will not cut the flab from your arms. Doing stomach crunches will not shrink your belly. And so on. Toning your muscles may improve the appearance of an otherwise chubby part of your body, but that’s all you can hope for. Incidentally, when you diet, the last place you gained fat is the first place you’ll lose it.

John Hunter wants to shoot stuff into space with a 3,600-foot gun. And he’s dead serious—he’s done the math. Making deliveries to an orbital outpost on a rocket costs $5,000 per pound, but using a space gun would cost just $250 per pound. Building colossal guns has been Hunter’s pet project since 1992, when, while a physicist at Lawrence Livermore National Laboratory, he first fired a 425-foot gun he built to testlaunch hypersonic engines. Its methane-driven piston compressed hydrogen gas, which then expanded up the barrel to shoot a projectile. Mechanical firing can fail, however, so when Hunter’s company, Quicklaunch, released its plans last fall, it swapped the piston for a combustor that burns natural gas. Heat the hydrogen in a confined space and it should build up enough pressure to send a half-ton payload into the sky at 13,000 mph.

Hunter wants to operate the gun, the “Quicklauncher,” in the ocean near the equator, where the Earth’s fast rotation will help slingshot objects into space. A floating cannon—dipping 1,600 feet below sea level and steadied by a ballast system—would let operators swivel it for different orbits. Next month, Hunter will test a functional, 10-foot prototype in a water tank. He says a full-size launcher could be ready in seven years, provided the company can round up the $500 million. Despite the upfront cost, Hunter says he has drawn interest from investors because his reusable gun saves so much cash in the long haul. Just don’t ever expect a ride in the thing: The gun produces 5,000 Gs, so it’s only for fuel tanks and ruggedized satellites. “A person shot out of it would probably get compressed to half their size,” Hunter says. “It’d be over real quick.” —AMINA ELAHI

HOW TO SHOOT STUFF INTO SPACE

STEP 1: HEAT ITThe gun combusts natural gas in a heat exchanger within a chamber of hydrogen gas, heating the hydrogen to 2,600°F and causing a 500 percent increase in pressure.

STEP 2: LET THE HYDROGEN LOOSEOperators open the valve, and the hot, pressurized hydrogen quickly expands down the tube, pushing the payload forward.

STEP 3: TO INFINITY AND BEYONDAfter speeding down the 3,300-foot-long barrel, the projectile shoots out of the gun at 13,000 mph. An iris at the end of the gun closes, capturing the hydrogen gas to use again.

A YACHT WITH AN ENORMOUS WING FOR A SAIL COULD WIN IT ALLAT THE AMERICA’S CUP RACE THIS MONTH

This year, the rules have all but disappeared for competitors in the world’s oldest international trophy competition, the America’s Cup sailing race. Motorized sails are fine, the single-hull rule is out, and in the case of the BMW Oracle Racing team’s boat, even sails are optional. Instead, the largest wing ever constructed could catch enough wind to make the yacht the fastest yet. Conventional fabric sails are unreliable. “Wind speed and direction change by the second,” says Mike Drummond, the design director for the BMW Oracle Racing team. “The crew must constantly maneuver the mainsail to maintain maximum speed.” A sail’s leading edge often ripples, particularly when tacking into the wind, increasing drag and causing the sail to lose the airfoil shape that helps propel the boat. In contrast, it takes just one sailor a few clicks on a computer to immediately swing the 190-foot-tall carbon-fiber-and-Kevlar wing into position, where it will hold its shape regardless of conditions. With the wing, Drummond says the 90-foot trimaran can sail up to 5 percent, or about one knot, faster. In the months leading up to the February 8 race day, Drummond’s team noticed a few drawbacks to the new design. In strong winds, where sailors would normally shrink a soft sail, the one-size wing can grab too much wind and destabilize the boat. And in choppy waters, the extra weight can cause the craft to pitch front to back. “Still, overall, it’s obvious that the boat goes faster,” Drummond says. “We used to measure performance gains in hundredths of a knot. Now we measure it in tenths of a knot or more.”—COREY BINNS

WINGThe 7,700-pound wing includes a single piece that rotates around the mast and eight flaps that catch or shed wind in different directions for thrust. Engineers claim that the wing—80 percent longer than a Boeing 747’s—can achieve twice the power of a soft mainsail.

MASTFiber-optic sensors in the mast and hull reflect light differently when stretched. A computer converts these changes into stress loads in real time to predict material failures and alert the crew if strong winds could snap the mast.

SAILA camera system photographs the soft sail, analyzes its shape and height, and compares the measurements with past performance data to suggest the optimal setup.

SMART SAILING Electronic sensors feed 26,000 data points every second—such as the wind speed, pitch of the waves, and stress on the boat—to a computer to calculate the optimum wing-sail configuration.

DIGITIZING THE TREE OF LIFE COULD FINALLY IDENTIFY THOUSANDS OF NEW SPECIES

Over the past 20 years, Richard Pyle figures he’s discovered 100 new species of fish. But he’s identified only one fifth of them. Pyle, an ichthyologist at Bishop Museum in Hawaii, isn’t a slacker—he spent hundreds of hours tracking down those fish. It’s just that proving that a new species is unique can be as tough as finding it in the first place.

“There are literally thousands of new species sitting in storage at museums,” says Quentin Wheeler, a renowned taxonomist and founder of the International Institute for Species Exploration at Arizona State University. Identifying these species isn’t just to satisfy curiosity; we need a clear understanding of species in order to best organize conservation efforts. Here’s the snag: To verify a new species, a taxonomist must examine the type specimens—the preserved representative samples of every known plant and animal—of each similar existing species to document the differences. Some animals must be compared with hundreds of specimens, and those might be anywhere in the world. Many are too fragile to ship. But Wheeler thinks he has a solution that could dramatically speed up the classification and identification of species.

This month, Wheeler and his collaborators at Microsoft and the Woods Hole Oceanographic Institution in Massachusetts applied for National Science Foundation funding to create digital type specimens—“e-types”—for the more than one million known insects. To generate an e-type, a curator will simply slide the bug into a custombuilt scanner that will take 100 or so 20-megapixel images and stitch them into a three-dimensional model using Microsoft’s Photosynth software. With a dozen of these machines working through the archives of the world’s natural-history museums, Wheeler expects that the effort could digitize all the insects in five years and, with additional funding and projects, the rest of the world’s 1.8 million known species within a decade. Every year, taxonomists introduce about 20,000 species. In the same period, an estimated 30,000 vanish. At that rate, the majority of Earth’s inhabitants could disappear before they’re known to science. Simply by making it easier to examine existing organisms, Wheeler says his project will help bump the species description rate to 200,000 a year—a clip that could make it possible to name the world’s commonly estimated 20 million unknown species within 50 years.

Some scientists, however, think even e-types won’t get the job done fast enough. Genetic testing, they argue, is the key. Leading this movement is Canadian evolutionary biologist Paul Hebert, who wants to assign every species a DNA “bar code” based on variations in a gene that nearly all organisms possess. A new species would be identified not by its physical divergence from existing type specimens but by the difference between its bar code and all the others. Because the system is fast and cheap—the technique requires basic laboratory skills and can process 95 samples in two hours for $10 apiece—Hebert says it could uncover every unknown plant and animal by 2025. But bar-coding is fast and cheap because it uses just one piece of one gene—and that makes it prone to errors. In 2008, Pyle made a definitive distinction between two new fish species, even though their bar codes were essentially identical. “It’s a blunt instrument,” Wheeler says of the DNA system. “One gene just isn’t sufficient.” Looking at actual specimens is an art, he says. Plus, it’s fun. Although he admits that someday it might be possible to define new species using only DNA, he doesn’t like that idea much: “That would make taxonomy too boring to be worth doing.”—PAT WALTERS

The 3-D thrill that swept movie theaters last year is now headed for your living room. In the wake of a new Blu-ray standard for high definition 3-D, Panasonic, Sony and Samsung are all releasing home-theater setups that can display 3-D movies in full high-def glory. Using a combo of 3-D-capable Blu-ray players, TVs and, yes, glasses, the systems are able to deliver separate, full-screen, 1080p pictures to each eye. The technique they use creates a picture as vivid as in a movie theater without requiring a major overhaul of TV technology. And within a few years, a new cable television standard could even bring live events like the Super Bowl right to your TV in high-def 3-D.—Corinne Iozzio

THE TVWe see depth when images from our left and right eyes merge into one; to re-create that in high-def, TVs must refresh the picture at least 120 times a second with alternating frames for the left and right eye, which tricks your brain into seeing only one image. Most new TVs are fast enough to do this, but to be 3-D-capable, TVs must include a converter chip and software to break down the signal and separate the left and right images. An infrared or radio beam syncs shutter glasses [below] with the screen to produce the final 3-D effect. Sony Bravia XBR-60LX900 Price not set; sonystyle.com

THE BLU-RAY PLAYERBlu-ray discs have plenty of room to store a separate 1080p signal for each eye (that’s twice as much information as in a 2-D movie), as well as the coding necessary to specify which image is meant for the left side and which for the right. 3-D-ready players use a special chip to interpret this info and send it to a 3-D-capable TV. Samsung BD-C6900 Price not set; samsung.com

THE GLASSESActive-shutter glasses, like those included in Panasonic’s system, rapidly block one eye at a time so that each eye sees only the frame meant for it. The glasses contain two small, black-and-clear LCD lenses that darken or lighten when a radio or infrared pulse from the TV (or an add-on emitter) signals that the image is changing. Panasonic Active-Shutter Glasses Price not set; panasonic.com

About Me

In its broadest sense, science (from the Latin scientia, meaning "knowledge") refers to any systematic knowledge or practice. In its more usual restricted sense, science refers to a system of acquiring knowledge based on scientific method, as well as to the organized body of knowledge gained through such research.

Fields of science are commonly classified along two major lines: natural sciences, which study natural phenomena (including biological life), and social sciences, which study human behavior and societies. These groupings are empirical sciences, which means the knowledge must be based on observable phenomena and capable of being experimented for its validity by other researchers working under the same conditions.